1. Field of the Invention
This invention relates generally to operational amplifiers and more particularly to a high precision operational amplifier which is intermittently operational and providing a low quiescent power requirement when in a standby state while providing a high slew rate when activated.
2. Description of Related Art
One of the challenges for wireless communications apparatus currently being developed and implemented with integrated circuits is to keep both active and standby power consumption low. For standby operation, circuits are turned on very briefly and then powered down as quickly as possible to minimize power consumption. However, for high precision analog circuit modules, such as analog to digital and digital to analog converters, reference voltage sources are often required for which large filter capacitors are employed to maintain low noise levels. In such instances, there are typically two choices for intermittent operation: (1) maintain buffering of the capacitor voltage between activity bursts; or (2) utilize a high slew rate to quickly recharge the capacitor at the beginning of each activity burst. The first option requires that reference and buffer circuits remain powered up continuously between bursts, while the second option requires that it must be possible to recharge the capacitor, typically in the range of 1 nF to 1 uF, quickly at the beginning of each activity burst. For some systems, the rapid recharge of the capacitor can require peak currents of 100 to 1000 times what is necessary to maintain the charge in normal operation. In both instances, power dissipation presents a formidable problem and in some instances can be excessive.